1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a filter module, and more particularly to a multi-band filter module available in various frequency bands and a method of fabricating the same.
2. Description of the Related Art
Recently, as telecommunication appliances represented by mobile phones are rapidly popularized, a demand for a thin and light filter for use in these appliances is also increased.
In particular, as the telecommunication appliances are miniaturized and complicated, there is a necessity for a small-sized terminal available in various frequency bands. In order to utilize various frequency bands, a multi-band filter is acutely needed to filter only required frequencies among signals received through one antenna. An existing method of implementing a multi-band filter by use of a ceramic filter has weak competitiveness in comparison with an FBAR (Film Bulk Acoustic Resonator) or a SAW (Surface Acoustic Wave) device in view of its size and property.
Up to now, the smallest device having a good frequency characteristic in the band of 2 GHz is the FBAR using the bulk acoustic characteristic, while the smallest device having a good performance in the band of 900 MHz is the SAW device using the surface acoustic characteristic.
The FBAR has the advantages of mass production and miniaturization. Also, the FBAR has a high quality factor that is a major property of a filter, and can be used in a micro frequency band, in particular, in the bands of a PCS (Personal Communication System) and a DCS (Digital Cordless System).
The FBAR is generally fabricated by sequentially depositing a lower electrode, a piezoelectric layer, and an upper electrode on a substrate. According to the operating principle of the BRAR device, an electric energy is applied to the electrodes to induce an electric field that is temporally varied in the piezoelectric layer, and then the electric field causes a bulk acoustic wave in the same direction as a vibration direction of a resonant part in the piezoelectric layer to generate resonance therein.
Both the FBAR and the SAW device utilize the RF characteristic by use of the acoustic resonance. However, the SAW device can obtain a good characteristic by use of a specific piezoelectric substrate only. In the case of the FBAR, although it is not limited to a substrate, a silicon substrate is generally used so as to be inexpensive, integrated and compatible with IC.
A common multi-band filter is generally fabricated by separately making the above filter devices and combining the same with chips and trimming circuits through additional package. The method of fabricating the multi-band filter by using a separate filter has the problems of a complicated construction, many defective factors such as a short circuit of a device, and an increased size thereof.
Accordingly, a need exists for a development of a multi-band filter module having a thin and simple construction and fabricated by a simple method.